test proxy supports CONNECT

There's a new 'http-proxy' server for tests that runs on a separate port
and lets clients do HTTP CONNECT to other ports on the same host to
allow us to test HTTP "tunneling" properly.

Test cases now have a <proxy> section in <verify> to check that the
proxy protocol part matches correctly.

Test case 80, 83, 95, 275, 503 and 1078 have been converted. Test 1316
was added.